Desilu was the television studio that made TOS up until its mid-second season when Paramount bought it up. The network simply bought and aired the show, and had creative input into it because they were paying for much of it -- but Desilu actually made the show, and was responsible for its existence in the first place. TOS was bought and its production overseen by Herbert F. Solow, Desilu's executive in charge of production. He also brought Mission: Impossible and Mannix to the air. TOS was filmed on Stages 9 and 10 of Desilu's studio facility and on the Culver City backlot owned by Desilu at the time, using Desilu-owned cameras and equipment and drawing on costumes and props from earlier Desilu productions (for instance, "A Piece of the Action" was written to allow reuse of costumes, cars, and gangster-era paraphernalia left over from Desilu's The Untouchables).
Desilu's studio was right next door to Paramount's, separated only by a wall. When Gulf + Western bought out Paramount and then Desilu, it combined the two studios into one under the Paramount name and tore down the wall between the studio lots. The westernmost 1/3 or so of Paramount Studios today, on the Gower Street side of the lot, is what used to be Desilu Studios (and before that was RKO Studios), and Desilu stages 9 and 10 are now Paramount stages 31 and 32. So all of TOS was made on what were originally Desilu's stages, using their equipment and most of their personnel, even after the studio was absorbed under the Paramount name.
So, yeah, Desilu is anything but a footnote. Star Trek wouldn't have existed without Desilu and Herb Solow.